Chlamydiae are obligate gram-negative intracellular prokaryotic pathogens that are responsible for significant human morbidity and infections of multiple organ systems. More than 90 million new cases of sexually transmitted, genitourinary Chlamydia trachomatis infection are reported annually. These infections are a significant cause of infertility, ectopic pregnancy, and chronic pelvic pain syndromes (Brunham, R. C. & Rey-Ladino, J. Nat Rev Immunol 5: 149-61 (2005)). Ocular infections with Chlamydia may result in trachoma, the primary cause of infectious blindness worldwide (see, Engel, J., Proc Natl Acad Sci USA 101: 9947-8 (2004)), and Chlamydia species also have been associated with other inflammatory diseases (see, Hannu, T., et al. Rheumatology (Oxford) 38: 411-4 (1999), Gencay, M., et al., Am J Respir Crit Care Med 163: 1097-100 (2001); Smieja, M., et al., BMC Infect Dis 2:21 (2002); and Dautry-Varsat, A., et al., Traffic 5: 561-570 (2004)). The pathophysiology of Chlamydial infections is only partly understood, in particular identification of host cellular proteins involved in Chlamydial infection that may reveal new strategies for disease control.
Chlamydia has a unique biphasic developmental cycle. The first step in infection requires attachment of a metabolically inactive but infectious, spore-like structure called the elementary body (EB). The initial reversible attachment of EB to epithelial cell layers is proposed to involve a number of Chlamydial and host ligands and adhesions. Possible candidates for attachment mediation include major outer membrane protein (MOMP), heat shock protein 70, OmcB, heparin sulfate-like glycosaminoglycans, polymorphic outer membrane protein gene family (pmp), estrogen receptor complex, and caveolae. Upon cellular attachment local actin polymerization, elicited by intracellular secretion of EB products and tyrosine phosphorylation of various protein species leads to endocytosis of the attached EB. After a few hours, an internalized EB differentiates into the reticulate body (RB), a metabolically active, non-infectious form which gives rise to >1000 progeny EBs, followed by host cell lysis and release of infectious EBs that begin another life cycle (see, Engel, J., Proc Natl Acad Sci USA 101, 9947-8 (2004); Dautry-Varsat, A., et al., Traffic 5: 561-570 (2004); Gabel, B. R., et al., Infect Immun 72: 7367-73 (2004); Davis, V. L., et al., Proc Natl Acad Sci USA 99: 9427-32 (2002); Raulston, J. E., et al., (2002) Infect Immun 70: 535-43 (2002); Finlay, B. B., et al., Science 276: 718-725 (1997); and Virok, D. P., et al., Infect Immun 73: 1939-46 (2005)).
Chlamydial infection can result from oral, vaginal, or anal sexual contact with an infected partner. Chlamydia trachomatis can be sexually transmitted. In women, the pathogen can cause pelvic inflammatory disease (PID) with a risk of tubal obstruction and infertility. In men, the bacteria can cause epidydimitis and infertility. Chlamydia can also cause acute respiratory tract infections in humans. Infection of the eye with Chlamydia trachomatis, or trachoma, is a leading cause of preventable blindness worldwide. Chlamydial infections are a particularly serious health threat to newborns who contract occular infections at birth from infected birth canals of their mothers. If untreated, almost 50% of these children develop inclusion conjunctivitis and 20% develop systemic infection resulting in serious pneumonia. Chlamydia also is likely to exacerbate atherosclerosis. In particular, coronary heart disease has been associated with increased titers of Chlamydia antibodies. In addition, reactive inflammatory arthritis is a common sequel to sexually acquired non-gonococcal genital tract infection. Approximately 50% of reactive inflammatory arthritis cases are associated with Chlamydia trachomatis infection of the genital tract. Chlamydial infection can be asymptomatic and irreversible damage may have already occurred before treatment is sought.
Accordingly, Chlamydia is a serious public health concern around the world. However, Chlamydia is an intracellular pathogen which is difficult to treat. There is no robust vaccine for Chlamydia and conventional antibiotic therapies often fail to clear chronic infections.
The epithelial membrane protein-2 (EMP2) is a member of the growth arrest specific-3/peripheral myelin protein-22 (GAS3/PMP22) family of tetraspan proteins. Other four-transmembrane families, connexins and tetraspanins, play roles in gap junctions, cell-cell recognition processes, and intracellular trafficking. Less is known about the GAS3/PMP22 family. The information available mainly relates to their potential roles in various diseases. For instance, mutations in the prototypic GAS3 family member PMP22 have been found to cause neurodegenerative disease (i.e., Dejerrine Sottas Syndrome and Charcot Marie Tooth Syndrome). EMP2 has also been implicated in B cell tumor progression and stress-induced apoptosis.
EMP2 is expressed at high levels in epithelial cells of the lung, eye, and genitourinary tracts. Like several tetraspan proteins (CD9, CD81, PMP22), EMP2 in murine fibroblasts is localized to lipid raft domains. EMP2 controls cell surface trafficking and function of certain integrins, GPI-linked proteins, and class I MHC molecules, and reciprocally regulates caveolin expression. (see, Claas, C., et al., J Biol Chem 276: 7974-84 (2001); Hasse, B., et al., J Neurosci Res 69: 227-32 (2002); Wadehra, M., et al., Exp Mol Pathol 74: 106-12 (2003); Wadehra, M., et al., Mol Biol Cell 15: 2073-2083 (2004); Wadehra, M., et al., J Biol Chem 277: 41094-41100 (2002); and Wadehra, M., et al., Clin Immunol 107: 129-136 (2003)).
Detailed studies of the subanatomic distribution of EMP2 in murine and human ocular tissue indicate that EMP2 is localized to epithelial layers of the cornea, ciliary body, and retinal pigmented epithelium-choroid, the stromal layers of the sclera, and the nerve fiber layer of the retina and optic nerve. This distribution is distinct from other TM4SF proteins and may relate to a role in apical membrane recycling.
Recent studies indicate that the interaction between Chlamydia and host cells occurs at specific cholesterol- and glycosphingolipids-rich lipid raft microdomains. Lipid rafts, often experimentally defined by their insolubility in cold non-ionic detergents are believed to be subspecialized cell membrane regions important in assembly of receptor signaling complexes, protein trafficking, endocytic and secretory pathways. Many other proteins associated with bacterial infection have been found in lipid raft compartments. Dautry-Varsat, A., et al., Traffic 5: 561-570 (2004); Simons, K., et al., Nature 387: 569-572 (1997); Gabel, B. R., et al., Infect Immun 72: 7367-73 (2004); Claas, C., et al., J Biol Chem 276, 7974-84 (2001); Brown, D. A., et al. J Biol Chem 275: 17221-4 (2000); and Subtil, A., et al., J Cell Sci 117: 3923-33 (2004); and Webley, W. C., et al., BMC Infect Dis 4: 23 (2004)
As reported herein, the Applicants have now surprisingly discovered that EMP2 is a molecular cell entry point for Chlamydia and that EMP2 polypeptides, anti-EMP2 antibodies, and EMP2 siRNA can modulate the ability of Chlamydia to enter a host cell to cause infection and disease. As discussed above, there remains a large need for methods and compositions which are useful in the prevention, treatment, and modulation of Chlamydia infection. Accordingly, this invention provides novel compositions and methods for meeting these and other needs.